There are many engine operating conditions that are either measured or estimated to improve internal combustion engine control. For example, manifold pressure is a common internal combustion engine parameter used in various engine control systems. To reduce system cost, it is known to estimate manifold pressure from engine mass air flow and engine speed along with known engine relationships. It is also common to improve accuracy of this estimated manifold pressure with manifold temperature and exhaust gas recirculation amounts.
Conversely, it is also known to estimate mass air flow from manifold pressure. Typically, measured manifold pressure, and also manifold temperature, are used with various predetermined engine maps and engine speed to estimate engine mass air flow. This estimated engine mass air flow can then be used to determine fuel injection amounts and various other parameters. It is further known to improve accuracy of engine mass air flow by including exhaust gas recirculation amounts.
In addition, it is also known to use throttle position and engine speed as indications of either mass air flow and/or manifold pressure.
The inventors have recognized a disadvantage with the above approaches. In particular, such estimation methods can have errors due to engine variation, engine aging, and various other effects. These potential errors can degrade engine performance, fuel economy, and emissions. For example, engine characteristics relating manifold pressure and mass air flow may change from one engine to another. Similarly, engine aging affects may change heat transfer characteristics, thereby causing errors to arise.